A tendency of deterioration in the quality of crude oils is more serious all over the world in recent years. Sulfur, nitrogen and aromatic compound contents in petroleum products are increasing. Obviously, said situation is sharply unsuitable for the requirement of increasingly strict environmental regulations. Hydrogenation is well known as one of the most efficient ways to improve the qualities of petroleum products. The hydrofining catalyst has become the most important and critical factor for such process. For this reason, many large companies go all out to carry out the work on further improving the existing hydrofining catalysts, and various hydrofining catalysts of better performance have been developed.
Distillate hydrofining catalysts commonly comprise metals or metal oxides having hydrogenation activity, certain acidic carriers and assistants. The metal components which are usually used are Co--Mo or Ni--Mo. Recently hydrofining catalysts which use Ni--W as active components are more popular. Further reducing the metal component contents in such catalysts and modifying their carrier characteristics in order to make it more suitable for hydrofining of inferior oils are the researching directions.
U.S. Pat. No. 3,779,903 discloses a process for the preparation of a hydrofining catalyst. Alumina sol is dried and then calcined to produce an alumina carrier having a pore volume between 0.15-0.45 ml/g. After that, the obtained carrier is impregnated with an aqueous solution containing tungsten and nickel, and then dried and calcined to produce the catalyst comprising 10-18% (wt.) nickel oxide, 25-40% (wt.) tungsten oxide and 1-9% (wt.) fluorine. Said catalyst due to high metal, especially nickel, contents has unduly high cost.
U.S. Pat. No. 4,330,395 discloses a process for the preparation of a hydrofining catalyst. This process comprises drying the starting materials based on tungsten compound and aluminium compound; calcining the resultant product; impregnating it with nickle compound; and then sulfiding and fluorinating the resultant product with sulfur compound and fluorine compound. The same disadvantage of this catalyst is unduly high metal contents and its preparation is also complicated.
Chinese Patent CN85,104,438B discloses a process for preparing hydrogenation catalyst. The boehmite of high purity which is prepared by hydrolysis of alkoxyl aluminium or alkyl aluminium is used as the precursor of catalyst carrier and the obtained hydrofining catalyst contains 1-5% (wt.) nickel oxide, 12-35% (wt.) tungsten oxide and 1-9% (wt.) fluorine. This catalyst has low metal contents and high hydrogenation activity. However, the price of this precursor used as catalyst carrier is much higher, resulting in high catalyst cost.
In addition, Chinese Patent Application No. 9410047.8 discloses a catalyst which is suitable for hydrofining heavy distillates. This catalyst comprises 1-5% (wt.) nickel oxide, 15-38% (wt.) tungsten oxide and 1-9% (wt.) fluorine, and its carrier is a modified alumina obtained by treatment at high temperature using air and water vapor, the pore distribution of this alumina is centralized within the range between 60-200 angstrom, but its preparation process is complicated and the energy consumption is high.
Purpose of the Invention
A purpose of the invention is to provide a hydrofining catalyst with lower cost and higher activity which is suitable for hydrogenation of various distillates.
Another purpose is to provide a process for the preparation of such hydrofining catalyst.